Thermodynamic analysis of hydrogen generation and retention in a portable hydrogen-rich water generator

Hydrogen-rich water (HRW) has attracted increasing interest because of the growing investigation of molecular hydrogen (H₂) in biomedical and wellness applications. This study experimentally and thermodynamically investigated hydrogen generation and dissolved hydrogen (DH) retention behaviour in a commercial portable HRW generator under varying headspace and temperature conditions. Under reference conditions, the generator produced DH concentrations of 1.95 ± 0.17 ppm. Smaller headspace fractions favoured higher retained DH concentrations because of elevated H₂ partial pressure within the sealed bottle. Increasing temperature increased electrolysis-driven H₂ generation, with water consumption increasing from 0.087 ± 0.016 g at 8°C to 0.136 ± 0.024 g at 38°C. However, retained DH increased only moderately because elevated temperature simultaneously reduced H₂ solubility. Thermodynamic energy and exergy analyses demonstrated that practical DH retention is governed by coupled interactions between H₂ generation, gas-liquid equilibrium behaviour, temperature, and headspace-controlled pressure conditions.